Nowadays, there are increased needs for effective use of water resources due to industrial developments and rise in population. For this, it is important to reuse wastewater such as industrial wastewaters. In order to reuse wastewater, it is necessary to refine water, that is, to separate foreign substances from water. As the method of separating foreign substances from water, there are various methods such as the membrane separation method, centrifugal separation method, activated carbon adsorption method, ozone treatment method and method of removing floating substances by coagulation. Removal of substances, which have a large influence on the environment, such as phosphorous and nitrogen contained in water and removal of oils and clay dispersed in water can be accomplished by using these methods.
Among these various water treating methods, the membrane separation method is one of the methods which are most usually used to remove insoluble substances in water. In this case, a filter aid is used in the membrane separation method from the viewpoint of protection of membrane and the viewpoint of raising the flow rate of water containing substances which can be hardly dehydrated.
On the other hand, as a method of removing harmful substances and valuable materials in water, a method is known in which substances dissolved in water are allows to undergo a given reaction to precipitate the substances, followed by solid-liquid separation. In conventional methods, copper ions are precipitated from water by a reaction and a polymer having an aggregation function is added to thereby aggregate the copper precipitate by the polymer, thereby separate and recover copper as a copper precipitate/polymer aggregate.
However, in the conventional method, the recovered copper precipitate/polymer aggregate itself contains a lot of polymer, and there is therefore the problem concerning a low copper purity per unit volume of the aggregate and hence a low copper recovery efficiency. Also, there is the problem that the amount of sludge (residue) left after copper is separated from the aggregate is large, resulting in increased amount of waste material, because the sludge is finally disposed of as waste material.